First find where the line intercepts on the y axis, then find the slope of the line by looking at how much the line goes up from each point. In this case, the line goes up by 2 and across by 1, so your slope will be 2/1 which is 2. (If the line went down, the slope would be -2/1 which is -2) Then you can plug in the numbers for the equation for y-intercept form y=mx+b which gives you y=2x+2
3 tables of 3rd graders times 4 chairs per table = 3*4 chairs or 12 chairs. 6 tables of 4th graders times 4 chairs per table = 6*4 chairs or 24 chairs.